Thomas & Betts Limitorque MX Device Net Field Unit manual Hardware interface, Network Cable

Limitorque MX DeviceNet Field Unit  FCD LMENIM2328-00 – 11/05

2.2.3Hardware interface

The DeviceNet Limitorque Interface is comprised of a minimum of one PCB with two interfaces - One for the DeviceNet Terminal Block connector and one for the SMT Main Board.

Figure 2.3 gives an overview about the hardware. The microcontroller on the DeviceNet Limitorque Interface handles the DeviceNet protocol, stores the DeviceNet parameters in an EEPROM, and commu- nicates with the SMT Main Board via SPI.

Figure 2.3 – DeviceNet Limitorque Interface

2.2.4Network Cable

DeviceNet is a CAN - based protocol that uses 5 wires including a shield. Two of the conductors are used for 24V DC power & up to 8 amps (4 amps for NEC Class 2) may be passed along the hi-way from a suitable power source. Two conductors are used for the CAN bus signals, CAN_H and CAN_L, which are usually smaller in diameter. Limitorque recommends Belden cable for connecting to a DeviceNet network. The specifications for thick and thin cable (per site requirements) are as follows:

Table 2.2 – Belden Cable Specifications

Belden

Part No.

AWG 

(Stranding)  dia. Inches  Nom. DCR

Insulation 

material  (color code)

Nominal 

O.D.

Nom 

Impedance 

(ohms)

Nominal 

Capacitance

Test  Maximum 

Frequency  Attenuation 

(MHz) dB/100ft

		2 – 15 AWG
		(19 x 28)	Power pair
		3.6 ohm/1000 ft	(Black/Red)				0.125	0.13
		11.8 ohm/km		12.2 mm
					120	12.0 pF/ft	0.5	0.25
	3082A
		2 – 18 AWG					1	1.36
		(19 x 30)	Data pair
		6.9 ohm/1000 ft	(Blue/White)
		22.7 ohm/km
		2 – 22 AWG
		(19 x 34)	Power pair
		17.5 ohm/1000 ft	(Black/Red)				0.125	0.29
		57.4 ohm/km
							0.5	0.50
12	3084A			7.2 mm	120	12.0 pF/ft
		2 – 18 AWG					1	1.70
		(19 x 36)	Data pair
		28.0 ohm/1000 ft	(Blue/White)
		91.9 ohm/km